: Perception has long been known to reflect the brain's ability to pool information from many different senses simultaneously. Therefore, it is surprising to note that comparatively little is known about the neural integration that takes place in the cortical neurons believed to underlie these perceptions, and virtually nothing is known about how their physiological properties are crafted during ontogeny. In the current proposal, we posit that early postnatal experience plays a critical role in determining the nature of these multi-sensory processes and their consequent impact on perception and behavior. These postulates will be examined here using neurons in the anterior ectosylvian sulcus (AES) and AES-mediated detection/identification and localization behaviors as models. The AES was targeted because of its high incidence of multi-sensory neurons, the prior demonstration that these neurons can integrate cross-modal information, and the involvement of this area in perception/behavior. In the first phase of this project we will examine the normal chronology with which somatosensory, auditory, visual and multi-sensory AES neurons develop, as well as the maturation of their ability to integrate cross-modal information. In the second phase of the project, we will utilize a multidisciplinary approach to examine what appears to be the most parsimonious hypothesis regarding the necessary and sufficient experiential antecedents of this fundamental information-processing capability: specifically, repeated experience with temporally coincident cross-modal (e.g., visual-auditory) cues. The proposed experiments will also examine whether these visual-auditory experiences must be obtained during early postnatal stages, or whether cross-modal experiences are capable of defining and modifying these neural processes throughout life.